This invention relates generally to a medium for cleaning a manual test interface while it is still in the prober. This manual interface is generally referred to as a probe card, which is used in the prober to make an electrical connection between the die on a silicon wafer and the tester so that the functionality of the die may be evaluated.
Currently, the method for cleaning the probe card is to remove it from the prober and manually clean the debris from the probe tips. The probe tips need to be cleaned to remove debris from them since the debris reduces the quality of the electrical circuit completed by the contact of the probe tips to any surfaces on a die. The completed electrical circuit is used to evaluate the electrical characteristics of the die by the test apparatus. The degradation of the quality of the electrical circuit caused by the probe tip debris may be interpreted by the test apparatus as a failure of the die under test even though the die is functioning correctly. This false failure of the die results in the rejection or the rework of good die thereby increasing the cost of the final products sold. In the industry, it has been seen that a 1% change in yield from an individual prober can equate to more than $1,000,000 per annum. Therefore, with thousands of probers operating worldwide, the impact to the industry from maintaining clean probes during testing can be very substantial.
Individual semiconductor (integrated circuit) devices are typically produced by creating multiple devices on a silicon wafer using well known semiconductor processing techniques including photolithography, deposition, and sputtering. Generally, these processes are intended to create multiple, fully functional integrated circuit devices prior to separating (singulating) the individual devices (dies) from the semiconductor wafer. However, in practice, physical defects in the wafer material and defects in the manufacturing processes invariably cause some of the individual devices to be non-functional, some of which may be repairable. It is desirable to identify the defective devices prior to separating or cutting the dies on the wafer. In particular, some product is actually repairable when the flaws are caught at the wafer lever. Other product may not be repairable but may be used in a downgraded application from the original product. This determination of the product""s capabilities ( a product definition provided by electrical probe testing) at the wafer level saves the manufacturer considerable cost later in the manufacturing process. In addition, product cost may be reduced if defective devices are identified.
To enable the manufacturer to achieve this testing capability a probe card, prober and tester are employed to make temporary electrical connections to the bonding pads, solder or gold bumps or any surface on the chip where connection can be made by making manual contact to that surface. The surface may be on the individual circuit device or on multiple circuit devices when the devices are still part of a wafer. Once the connections between the tester and the circuit device are made, power and electrical signals are transferred from the tester to the device for testing, to determine its functionality and to identify its acceptance or rejection for further processing. Typically, the temporary connections to the device bonding elements are made by contacting multiple electrically conductive probes (needle like structures) against the electrically conductive bonding elements of the device. By exerting controlled pressure (downwards force on the bonding pads) of the probe tips against the bonding pads, a satisfactory electrical connection is achieved allowing the power, ground and test signals to be transmitted.
The tester and prober need a manual interface to the bonding elements on the die to achieve contact. A probe card having a plurality of probes is used to make the connection with the bonding pads of the semiconductor die. The probes may be cantilever beams or needles or vertical beams. Typically, each probe is an inherently resilient spring device acting as a cantilever beam, or as an axially loaded column. A variation is to mount multiple probes in a spring-loaded support. In a conventional prober, the probe card, and its multiple probes, are held in precise mechanical alignment with the bonding elements of the device under test (or multiple devices, or wafer as the case may be) and the device is vertically translated into contact with the tips of the probes. In the typical prober, the tips of the probes may perform a scrubbing action in which the tip of the probes moves horizontally as it contacts the bonding pad in order to scrub away oxide, or any other material on the pad, that may inhibit the electrical contact between the probes and the bonding pads. Although the scrubbing action improves the electrical contact between the probe tip and the bonding pad, it unfortunately also generates some debris (the scraped up oxide or other debris) that may also prevent the probe tip from making a good electrical contact with the bonding pad. Alternatively, the probe tip may press vertically into the bonding pad, solder or gold bump with sufficient force to penetrate any surface material and establish good electrical contact. The probe tip may become contaminated with contaminates such as aluminum, copper, lead, tin or gold.
Typically, the debris generated by probing needs to be periodically removed from the probe elements to prevent a build-up which causes increased contact resistance, continuity failures and false test indications, which in turn results in artificially lower yields and subsequent increased product costs. Typically, the entire probe card with the plurality of probes must be removed from the prober and cleaned or abrasively cleaned in the prober. In a typical prober, the probe card is cleaned as often as several times an hour.
The process of cleaning in the prober using an abrasive pad burnishes the tips but it does not remove the debris. The burnishing actually causes wear to the probe card by shortening the probe tips. In addition, since it does not remove the debris, and since the debris exhibits a slight electrical charge, it attracts more debris so the probe card will require cleaning more often than the original clean card. Currently the debris from burnishing can be removed manually by means of alcohol and a cotton tip swab or an air gun. Each method cleans the probes but requires stopping the prober and a person to perform the function.
Other contaminates, such as lead and tin, may be removed by abrasive cleaning/burnishing or cleaning the probes with a solution that may typically be an acid for example. When probe cards which have collected lead and tin are burnished, particulates of lead are released into the air that cause environmental hazards. In addition, the acid solution requires a separate, rather expensive machine that sprays the solution onto the tips in a closed chamber. These typical cleaning processes are expensive since the tester will have down time and a replacement card must be purchased to run while the other probe card is being cleaned. In addition the equipment and manual labor adds additional costs to the task performed.
It is desirable to provide a probe card cleaning device and method which overcomes the above limitations and drawbacks of the conventional cleaning devices and methods so that the probe cards may be cleaned more rapidly and effectively while in the prober and it is to this end that the present invention is directed. The cleaning device and method may also be used with other devices.
In accordance with the invention, a cleaning medium is provided that will clean the probes of a probe card without removing the probe card from the prober. In particular, the cleaning medium may be placed within the prober similar to a wafer being tested so that the probes of the probe card contact the cleaning medium periodically to remove debris and/or contaminates from the probes. In a preferred embodiment, the cleaning medium may include a substrate that may be shaped like a typical semiconductor wafer that typically fits into the prober. The substrate may also be a ceramic plate or any type of substrate, which can fit over or replace the abrasive plate in the prober. The pad may have predetermined mechanical and/or chemical characteristics, such as abrasiveness, density, elasticity, tackiness, planarity, and/or chemical properties, such as being acetic or basic, so that when the probe tips contact the pad surface, the tips of the probes are cleaned and the debris and contaminates are removed from the tips. In another embodiment, the pad may be made of a material so that the probe tips may penetrate into or through the pad, which cleans the debris from the tips. In a preferred embodiment, the substrate may be a semiconductor wafer, ceramic, or any material to which the cleaning pad will attach. In another embodiment, the physical properties of the pad, such as density and abrasiveness, may be predetermined so as to clean the probe element and remove bonded or embedded debris from the probe elements without causing significant damage to the probe elements. In another embodiment, the physical properties of the pad, such as density and abrasiveness, may be predetermined so as to shape or reshape the probe elements during probing on or into the medium.
Thus, in accordance with the invention, a cleaning medium for cleaning probe elements in a semiconductor testing apparatus is provided wherein the cleaning medium comprises a substrate having a configuration to be introduced into the testing apparatus during normal testing operation, and a pad, secured to the substrate. The pad has predetermined characteristics, which clean debris from the probe elements and maintain or modify the shape of the probe element when the elements contact or penetrate into or through the pad.
In accordance with another aspect of the invention, a method for cleaning the probe elements on a prober or an analyzer is provided wherein the method comprises loading a cleaning medium into the prober, the cleaning medium having the same configuration as the wafers with the semiconductor dies normally tested by the testing apparatus and the cleaning medium having a top surface with predetermined properties, such as abrasiveness, tack, hardness, that clean the probes. The method further comprises contacting the probe elements with the cleaning medium during the normal testing operation in the prober so that any debris is removed from the probe elements during the normal operation of the prober or analyzer.
In accordance with another aspect of the invention, a method for maintaining or modifying the shape of the probe elements on a prober or an analyzer is provided wherein the method comprises loading a cleaning medium into the prober or analyzer, the medium having varying density, tack, abrasiveness or other physical characteristics which are optimized for various probe elements of the probe cards.